@article{SchickLeGuyaderPontiusetal.2016,
  author    = {Schick, Daniel and Le Guyader, Loic and Pontius, Niko and Radu, Ilie and Kachel, Torsten and Mitzner, Rolf and Zeschke, Thomas and Schuessler-Langeheine, Christian and F{\"o}hlisch, Alexander and Holldack, Karsten},
  title     = {Analysis of the halo background in femtosecond slicing experiments},
  series = {Journal of synchrotron radiation},
  volume    = {23},
  journal   = {Journal of synchrotron radiation},
  publisher = {International Union of Crystallography},
  address   = {Chester},
  issn      = {1600-5775},
  doi       = {10.1107/S160057751600401X},
  pages     = {700 -- 711},
  year      = {2016},
  abstract  = {The slicing facility FemtoSpeX at BESSY II offers unique opportunities to study photo-induced dynamics on femtosecond time scales by means of X-ray magnetic circular dichroism, resonant and non-resonant X-ray diffraction, and X-ray absorption spectroscopy experiments in the soft X-ray regime. Besides femtosecond X-ray pulses, slicing sources inherently also produce a so-called `halo' background with a different time structure, polarization and pointing. Here a detailed experimental characterization of the halo radiation is presented, and a method is demonstrated for its correct and unambiguous removal from femtosecond time-resolved data using a special laser triggering scheme as well as analytical models. Examples are given for time-resolved measurements with corresponding halo correction, and errors of the relevant physical quantities caused by either neglecting or by applying a simplified model to describe this background are estimated.},
  language  = {en}
}
@article{PontiusBeyeTrabantetal.2018,
  author    = {Pontius, Niko and Beye, Martin and Trabant, Christoph and Mitzner, Rolf and Sorgenfrei, Nomi and Kachel, Torsten and Woestmann, Michael and Roling, Sebastian and Zacharias, Helmut and Ivanov, Rosen and Treusch, Rolf and Buchholz, Marcel and Metcalf, Pete and Schuessler-Langeheine, Christian and F{\"o}hlisch, Alexander},
  title     = {Probing the non-equilibrium transient state in magnetite by a jitter-free two-color X-ray pump and X-ray probe experiment},
  series = {Structural dynamics},
  volume    = {5},
  journal   = {Structural dynamics},
  number    = {5},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {2329-7778},
  doi       = {10.1063/1.5042847},
  pages     = {8},
  year      = {2018},
  abstract  = {We present a general experimental concept for jitter-free pump and probe experiments at free electron lasers. By generating pump and probe pulse from one and the same X-ray pulse using an optical split-and-delay unit, we obtain a temporal resolution that is limited only by the X-ray pulse lengths. In a two-color X-ray pump and X-ray probe experiment with sub 70 fs temporal resolution, we selectively probe the response of orbital and charge degree of freedom in the prototypical functional oxide magnetite after photoexcitation. We find electronic order to be quenched on a time scale of (30 +/- 30) fs and hence most likely faster than what is to be expected for any lattice dynamics. Our experimental result hints to the formation of a short lived transient state with decoupled electronic and lattice degree of freedom in magnetite. The excitation and relaxation mechanism for X-ray pumping is discussed within a simple model leading to the conclusion that within the first 10 fs the original photoexcitation decays into low-energy electronic excitations comparable to what is achieved by optical pump pulse excitation. Our findings show on which time scales dynamical decoupling of degrees of freedom in functional oxides can be expected and how to probe this selectively with soft X-ray pulses. Results can be expected to provide crucial information for theories for ultrafast behavior of materials and help to develop concepts for novel switching devices. (C) 2018 Author(s).},
  language  = {en}
}
@article{ThielemannKuehnSchickPontiusetal.2017,
  author    = {Thielemann-K{\"u}hn, Nele and Schick, Daniel and Pontius, Niko and Trabant, Christoph and Mitzner, Rolf and Holldack, Karsten and Zabel, Hartmut and F{\"o}hlisch, Alexander and Schuessler-Langeheine, Christian},
  title     = {Ultrafast and Energy-Efficient Quenching of Spin Order: Antiferromagnetism Beats Ferromagnetism},
  series = {Physical review letters},
  volume    = {119},
  journal   = {Physical review letters},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {0031-9007},
  doi       = {10.1103/PhysRevLett.119.197202},
  pages     = {6},
  year      = {2017},
  abstract  = {By comparing femtosecond laser pulse induced ferro- and antiferromagnetic dynamics in one and the same material-metallic dysprosium-we show both to behave fundamentally different. Antiferromagnetic order is considerably faster and much more efficiently reduced by optical excitation than its ferromagnetic counterpart. We assign the fast and extremely efficient process in the antiferromagnet to an interatomic transfer of angular momentum within the spin system. Our findings imply that this angular momentum transfer channel is effective in other magnetic metals with nonparallel spin alignment. They also point out a possible route towards energy-efficient spin manipulation for magnetic devices.},
  language  = {en}
}
@misc{SchickEckertPontiusetal.2016,
  author    = {Schick, Daniel and Eckert, Sebastian and Pontius, Niko and Mitzner, Rolf and F{\"o}hlisch, Alexander and Holldack, Karsten and Sorgenfrei, Nomi},
  title     = {Versatile soft X-ray-optical cross-correlator for ultrafast applications},
  series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {1331},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-43696},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436962},
  pages     = {054304-1 -- 054304-8},
  year      = {2016},
  abstract  = {We present an X-ray-optical cross-correlator for the soft (> 150 eV) up to the hard X-ray regime based on a molybdenum-silicon superlattice. The cross-correlation is done by probing intensity and position changes of superlattice Bragg peaks caused by photoexcitation of coherent phonons. This approach is applicable for a wide range of X-ray photon energies as well as for a broad range of excitation wavelengths and requires no external fields or changes of temperature. Moreover, the cross-correlator can be employed on a 10 ps or 100 fs time scale featuring up to 50\% total X-ray reflectivity and transient signal changes of more than 20\%. (C) 2016 Author(s).},
  language  = {en}
}
@article{SchickEckertPontiusetal.2016,
  author    = {Schick, Daniel and Eckert, Sebastian and Pontius, Niko and Mitzner, Rolf and F{\"o}hlisch, Alexander and Holldack, Karsten and Sorgenfrei, Nomi},
  title     = {Versatile soft X-ray-optical cross-correlator for ultrafast applications},
  series = {Structural dynamics},
  volume    = {3},
  journal   = {Structural dynamics},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {2329-7778},
  doi       = {10.1063/1.4964296},
  pages     = {054304-1 -- 054304-8},
  year      = {2016},
  abstract  = {We present an X-ray-optical cross-correlator for the soft (> 150 eV) up to the hard X-ray regime based on a molybdenum-silicon superlattice. The cross-correlation is done by probing intensity and position changes of superlattice Bragg peaks caused by photoexcitation of coherent phonons. This approach is applicable for a wide range of X-ray photon energies as well as for a broad range of excitation wavelengths and requires no external fields or changes of temperature. Moreover, the cross-correlator can be employed on a 10 ps or 100 fs time scale featuring up to 50\% total X-ray reflectivity and transient signal changes of more than 20\%. (C) 2016 Author(s).},
  language  = {en}
}